In lawn mowers, including walk-behind lawn mowers, it is often desirable to provide means for propelling the lawn mower other than by the user. Such lawn mowers are typically known as self-propelled lawn mowers. Although self-propelled lawn mowers have significant advantages, disadvantages arise in that such units tend to be costlier, heavier, and more difficult to maintain than comparable lawn mower which are not self-propelled. Therefore there is always a need to provide self-propelled lawn mowers which are less expensive, lighten, and easier to maintain.